A GMO creeping bentgrass plant grows in an onion field south of Ontario, Ore., last year. The grass, which was genetically modified by Scotts Miracle-Gro Co. to resist glyphosate, escaped from field trials in 2003 and has taken root in Malheur and Jefferson counties in Oregon and part of Canyon County in Idaho.

ONTARIO, Ore. — Scotts Miracle-Gro Co. is reporting a large decline in the number of genetically modified creeping bentgrass plants in Malheur County.

The plant, used on golf courses, was genetically engineered by Scotts and Monsanto Co. to withstand applications of glyphosate, the active ingredient in Monsanto’s Roundup weed killer.

It took root in Oregon’s Malheur and Jefferson counties after escaping field trials in 2003. A small number of the plants have also been detected in Canyon County, Idaho.

Some farmers and irrigation districts worry the plants could clog irrigation ditches and affect shipments of crops to nations that don’t accept traces of genetically modified organisms, or GMOs.

Danielle Posch, a senior research specialist with Scotts, told members of the Idaho-Oregon onion industry during their annual meeting last week that the number of GMO bentgrass plants found in Malheur County last fall dropped by 42 percent compared to the same time in 2016.

“In 2017, we saw a significant reduction in the total number of glyphosate-tolerant creeping bentgrass plants,” she said.

Similar data for Jefferson County isn’t yet available.

Posch said the reduction in Malheur County was likely due to the Environmental Protection Agency’s approval last year of a special local need label for the use of glufosinate to control the plant.

Glufosinate is the most effective herbicide for controlling the GMO bentgrass but before the special need label, it couldn’t be used over waterways.

The plants require nearly constant moisture and can be found mostly near canals and irrigation ditches. But before the label was issued, glufosinate could only be used during a short window before and after the canals were dry.

The plants are harder to kill during those times because they aren’t growing and taking up the chemical, Posch said.

She said the company is cautiously optimistic that the use of glufosinate during the growing season is the reason for the large reduction in the number of GTCB plants.

“It makes biological sense that the chemical would be making the significant difference,” Posch said. “It’s been a great tool for us.”

Being able to use glufosinate over waterways has made a huge difference in the battle to control the plant, said Malheur County farmer Les Ito, a member of a working group of farmers, irrigation district representatives and others that is coordinating with Scotts in its efforts to control the plant.

“We needed something that could work at the water level,” he said.

Ito said he was initially skeptical about Scotts’ commitment to control the plant, but the company so far is living up to its word.

“We all feel we need to continue to hold Scotts accountable,” he said. “But they are following through on what they said they would do and I believe they have our best interests in mind. I feel a lot better about it than I did before.”

Ito said it’s unlikely the plant will ever be eradicated from the county “but we can manage it pretty well and we’ll need their help.”